Particularly well-known examples of electrochemical cells are button cells and round cells. Button cells usually have a cylindrical housing, the height of which is equal to or less than its diameter. In round cells, the housing is likewise cylindrical, but its height exceeds its diameter.
It is possible for very different electrochemical systems to be present in the housings. Very widespread cells are those based on zinc/air, zinc/MnO2 and nickel/zinc. Secondary (rechargeable) systems are also widespread. Examples of these are nickel/metal hydride cells, nickel/cadmium cells and lithium ion cells.
The cylindrical housing of round cells and button cells conventionally consists, in general, of two solid, usually metallic housing parts, between which there is arranged an electrically insulating seal. One of the housing parts electrically connects to the positive electrode and has correspondingly positive polarity. The other electrically connects to the negative electrode and has correspondingly negative polarity. The seal is intended to prevent electrical contact between the housing parts having opposite polarity. Furthermore, it is intended to counteract escape of liquid and moisture from the housing and penetration thereof into the housing.
The use of metallic housings is associated with various disadvantages. They are produced by a complex deep drawing method, and corrosive attack on the housing by the electrolyte or by other corrosive substances formed in the charging and discharging operation can never be entirely ruled out in spite of specific precautions.